Control means for public works machine

ABSTRACT

An earthworking machine having separate hydraulic drive motors for front and rear wheels and a hydraulic cylinder for lifting or lowering a forwarding extending work bucket is disclosed with work fluid for the cylinder being provided solely through a three-position regulator valve having both a manually operable positioning member and an automatically operable positioning means responsive to differences in hydraulic feed pressure to the drive motors for effecting a raising or lowering of the work bucket to maintain the front and rear wheels in ground contact; in a first embodiment the control valve is directly actuated by hydraulic feed fluid from the inputs to the vehicle drive motors and in a second embodiment, pilot fluid is provided through a regulator operated by the feed motor fluid to the three-position regulator valve.

Leroux 1451 Sept. 16, 1975 CONTROL MEANS FOR PUBLIC WORKS MACHINE Primary Examiner-Frank E. Werner Assistant Examiner-Ross Weaver [75] Inventor: Jean l Le Attorney, Agent, or Firm-Mason, Fenwick &

Plessis-Bellevllle, France L awrence [73] Assignee: Societe Anonyme: Poclain, Le

Plessis-Belleville, France [57] ABSTRACT 22 Filed; Jan. 31 1974 An earthworking machine having separate hydraulic drive motors for front and rear wheels and a hydraulic [211 App!" 438378 cylinder for lifting or lowering a forwarding extending work bucket is disclosed with work fluid for the cylin- 301 Foreign Application p i i D m der being provided solely through a three-position reg- Feb. 9, 1973 France 73.04754 P valve having both a manually operable 9 lng member and an automatlcally operable posltlomng 52 us. 01 214/762; 214/771 means responsi"? differences in l f i9 feed [51] Int. Cl. E02F 3/85 presslfre to the dnve motors for ef feCt mg a rdlsmg or 58 Field of Search 214/138, 140, 762, 771, lowermg of F work bucket P and 21 4/778 rear wheels in ground contact; In a first embodiment the control valve is directly actuated by hydraulic feed [56] References Cited fluid from tlclle inptljitsdto thf velllitilefldr ige motors gng in a secon em 0 imen pl 0 ul 1s provi e UNITED STATES PATENTS through a regulator operated by the feed motor fluid 3,542,228 11/1970 Horsch 214/762 to the three position regulator Valvg 3,583,585 6/1971 Joyce .1 214/762 0 3,782,572 1/1974 Gautier 214/762 6 Claims, 4 Drawing Figures K i II My g 12 l3 l5 1 a AMER I6 27,, 26 29 30 ,25 26 1 l g 1. 1 33- -37 l; 1 t? \l';\ 20

PATH-H551 SEP] 6 19. 5 I 3 9 O5 5 SHEETIOFZ CONTROL MEANS FOR PUBLIC WORKS MACHINE The present invention is concerned with improvements in and relating to public work machines and in particular with improvements in machines. adapted to use the method described in US. Pat. No. 3,782,572.

According to the present invention there is provided a public works machine comprising:

a frame, l

a set of front driving wheels to which at least one first hydraulic driving motor is coupled;

a set of rear driving wheels to which-at least one rear hydraulic driving motor is coupled;

means for supplying fluid under pressure to said front and rear motors and connected thereto by respective feed pipes;

discharge reservoir means;

working equipment articulated to said frame;

a double-acting drive member coupled between said frame and said working equipment and which comprises two chambers;

a first pipe and a second pipe connected respectively to said two chambers;

a three-position regulator which:

in a first position connects said first pipe to said fluid supply means and said second pipe to said discharge reservoir means; I

in a second position connects said first pipe to said discharge reservoir means and said second pipe to said fluid supply means;

and, in a third position blocks sa'id first and second pipes;

manually operable means for selecting the position of said regulator; v

and, automatically operable means-for selecting the position of said regulator in dependance on the values of the torques opposing said front and rear sets of wheels and comprising a double-acting drive device having two chambers which are connected respectively to a third pipe and a forth pipe which can be placed in communication respectively with fluids at pressures corresponding to those in said feed pipes to said front and rear motors, and a return member tending to maintain said regulator in its third position when the effects of the pressures of fluids in said two chambers are equal and opposite.

In one embodiment the machine also comprises a two-position regulator, in the first position of which corresponds to effective operation of said automatically operable means, communication can be established between said two chambers of said drive device and fluids at pressures corresponding to those in said feed pipes to said front and rear motors, and in the second position of which, which corresponds to the placing of said automatically operable means out of operation, said two chambers of the drive device are placed in communication with said discharge reservoir means.

The feed pipes to said front and rear motors may be connected respectively by said third and fourth pipes to said two chambers of said drive device. 2

In this case said two-position regulator. is preferably interposed between said third and fourth pipes and said feed pipes. In its first positionit places said third and fourth pipes in communication with said feed pipes, and in its second position it places said third and fourth pipes in communication with said discharge reservoir 1 ,-.In a: secondembodiment the machine comprises a secondlthree position regulator to which is coupled a second automatically operable means for selection of thejposition'pf the second three-position regulator in I merriber tending to maintain said second regulator in its third position, when the effects of the pressure of fluids in saidtwofchambers are equal and opposite said two chambers of said second automatically operable device being connected respectively by pipes to said feed pipes to' said front and rear motors, and wherein said third *andfourth pipes are connected to said second three-position regulator, a fifth pipe connected to means forsupplying fluid under pressure and a sixth pipe conirected to a discharge reservoir are connected to said second three-position regulator, the three positions of said second three-position regulator correspond to the preponderance of the effect of fluid in one or other of said chambers of said second automatically operable means, or with equality of the said effects, and said second three-position regulator connects said third pipe to said fifth pipe and said fourth pipe to said sixth pipe initsfir st position, said third pipe to said sixth pipe and saidlfourth pipe to said fifth pipe in its second position' and said third and fourth pipes to said sixth pipe in its third position.

' Advantage'ously in this machine said two-position regulatordsrarranged in said fifth pipe which it separates intotwo portions and is connected by a seventh pipe to.-said;discharge reservoir means, in its first position said two-position regulator places said two portions of said .fifth pipe to which it is connected in communication in its second position said two-position regulatorisolates said two portions of the fifth pipe from one another. and places said seventh pipe in communication with that one of said two portions of said fifth pipe which'is, connected to said second three-position regulator.-

'Theqinvention will be better understood from the following-description of an embodiment thereof, given below byway of example only, with reference to the accompanying drawings, in which:

FIGS land 2 illustrates diagrammatically a machine of the loader. type during two phases of use;

FIG. 3 shows the hydraulic circuit of an embodiment of a machine in accordance with the invention; and

FIG.,4 shows the hydraulic circuit of another embodiment of a machine in accordance with the invention I A publicworks machine, such as a loader, may in a first phase of use tend to adopt the position shown in FIG. 1. As the machine moves forward, the bucket l bears on material 2 but does not succeed in penetrating into the material. The force of the reaction of the material 2 against the bucket 1 is transmitted by the working equipment 31 0 the frame 4 of the machine with the result that the front wheels 5 of the machine tend to lose contact with the ground 6.

In anotherph ase of use illustrated in FIG. 2 when, for example, the bucket 1 tries to lift all or a portion of the material 2 the rear wheels 7 of the machine tend to lift from the ground 6.

As shown in FIGS. 1 and 2, a double-acting jack 8 is coupled between the working equipment 3, which is articulated on the frame 4 for pivotal movement about the axis 9, and the said frame 4. To this end the pistonrod of the jack is articulated on the working equipment 3 for pivotal movement about the axis 10 and the cylinder is articulated on the frame 4 for pivotal movement about axis 11.

In one embodiment of the invention shown in FIG. 3 the two chambers 12 and 13 of the jack are connected to a first three-position regulator 14 respectively by a first pipe 15 and a second pipe 16. The regulator 14 is in turn connected by pipes 17 and 18 to a hydraulic pump 19 and a discharge reservior 20 respectively. The movable member of the regulator 14 has three positions as follows:

in the first position the pipe 15 is placed in communication with the pipe 17 and the pipe 16 with the pipe 18,

in the second position, the pipe 15 is placed in communication with the pipe 18 and the pipe 16 with the pipe 17, and

in the third position the pipe 17 is placed in communication with the pipe 18 and the pipes 15 and 16 are blocked at the regulator.

Also shown in FIG. 3 are the hydraulic driving motor or motors 21 for the front wheels and the hydraulic driving motor or motors 22 for the rear wheels. Each of these motors comprises two chambers capable selectively of being put in communication with a pump 23, 24 respectively and with the discharge reservoir 20 by means of manually operatable regulators 25, 26 which may, if required, be coupled. These regulators each have three positions. They are connected to the two chambers of the respective motor by two pipes, the regulator 25 by the pipes 27 and 28 to the motor 21, the regulator 26 by the pipes 29 and to the motor 22, and to the pumps 23, 24 and the reservoir 20, the regulator 25 by the pipes 31 and 32, the regulator 26 by the pipes 33 and 34. In the first position of each regulator 25, 26 the pipes 27 and 31, 28 and 32, 29 and 33, 30 and 34 are placed in communication. In the second positions of these regulators the pipes 27 and 32, 28 and 31, 29 and 34, 30 and 33 are placed in communication. Finally, in the third positions of the regulators 25 and 26 the pipes 31 and 32 and 33 and 34 are placed in communication and the pipes 27, 28, 29 and 30 are blocked at the regulators.

It will be observed that the regulator 14 is provided with a lever 35 for optional manual, as shown, or pedal control of the positiin of its movable member. In addition the regulator 14 is coupled to a resilient member 36 which acts to bias the movable member of the regulator 14 to its third position, and to a double-acting jack indicated diagrammatically by the chambers 37 and 38, the action of fluid under pressure capable of being contained in the chambers 37, 38 being opposite that of the resilient member 36.

A two-position regulator 39 is connected by pipes 40 and 41 to the chambers 37 and 38 respectively, and by pipes 42 and 43 to the delivery pipes 31 and 33 respectively, from the pumps 23 and 24. A pipe 44 connects the regulator 39 to the reservoir 20.

The regulator 39 has a manual control 45. The two positions of its movable member are as follows:

in the first position, the pipes 41 and 42, 40 and 43 are placed in communication and the pipe 44 is blocked at this regulator;

in the second position, the three pipes 40, 41 and 44 are placed in communication and the pipes 42 and 43 are blocked at this regulator.

It is to be observed that pipes 46 connect the delivery pipes 17, 31, 33 of the various pumps to the reservoir 20 by means of pipes 18, 32 and 34, respectively, a calibrated discharge valve 47 being arranged in each of the pipes 46.

In the embodiment of FIG. 4 a number of the members already described with reference to FIGS. 1 to 3 are again found. Similar members are indicated by the reference numbers used in FIGS. 1 to 3.

In this embodiment the pipe 18 consists of two sections 18a and 18b which are connected to the distributor 14, a non-return valve 48 being arranged in the section 18a of the said pipe 18, which is tapped off from the delivery pipe 17 from the pump 19. The section 18b is connected to the reservoir 20. The non-return valve 48 enables flow of the fluid from the pump 19 towards the regulator 14 through the pipe 18a.

The three positions of the regulator 14 are therefore as follows;

in the first position, the pipes 15 and 17 and the pipes 16 and 18b are placed in communication the pipe 18a is blocked at the regulator 14; i

in the second position, the pipes 15 and 18b and the pipes 16 and 17, are placed in communication and the pipe 18a is again blocked at the regulator 14; and

in the third position, the pipes 18a and 18b are placed in communication, and the pipes 15, 16 and 17 are blocked at the regulator Another three-position regulator 49 is coupled to a resilient member 50 which acts to bias the movable member of the regulator 49 into one of its positions, called the third position or mean position, and to a double-acting jack indicated diagrammatically by the chambers 51 and 52, the action of fluid under pressure capable of being contained in the chambers 51, 52 being opposite to that of the resilient member 50. The chambers 51 and 52 are connected by pipes 53 and 54 to the delivery pipes 31 and 33 from the pumps 23 and 24 respectively. In addition a pipe 62 connects the regulator 49 to the reservoir 20.

A two-position regulator 55 is connected to the delivery pipe 56 from a low-pressure pump 57, and to the reservoir 20 by a pipe 58. Finally, a pipe 59 connects the regulators 49 and 55. The pump 57 is connected to the reservoir 20 by its suction pipe 60, and a pipe 46 is tapped off from the delivery pipe 56 and is connected to the reservoir 20, a calibrated discharge valve 47 being arranged in the pipe 46. The regulator 55 is provided with a manual controller 61 for controlling the position of its movable member.

The three positions of the regulator 49 are as follows:

in the first position, the pipes 40 and 59 and 41 and 62 are placed in communication;

in the second position, the pipes 40 and 62 and 41 and 59 are placed in communication; and

in the third position, the three pipes 40, 41 and 62 are placed in communication, and the pipe 59 is blocked at the regulator 49.

The two positions of the regulator 55 are as follows:

in the first position, the pipes 56 and 59 are placed in communication and the pipe 58 is blocked at the regulator 55, and

in the second position, the pipes 58 and 59 are placed in communication and the pipe 56 is blocked at the regulator 55.

The pumps 19, 23 and 24 are again connected to the reservoir by suction pipes 63.

From the following explanation of the operation of the above described machines, the advantages that such machines offer, and the progress that they represent with respect to known machines, will become apparent. In order to simplify the explanation, only the operation of the machine while running forwards will be considered. v

Firstly the operation of the circuit described with reference to FIG. 3 will be examined. It is assumed that the regulator 39 is initially in its first position. When the machine tends to adopt the position of FIG. 1 and when therefore the bearing load of the front wheels on the ground 6 is reduced, the relative torque opposing the wheels 5 is likewise reduced. A drop in pressure is observed in the fluid in the feed pipe 27 to the motors 21 of the front wheels 5 as well as in the delivery pipe 31 from the pump 23 connected to the pipe 27. The pressure in the pipes 42 and 41, which are connected to the pipe 31, is likewise low. If there is still good adhesion between the rear wheels 7 and the ground the pressures in the pipes 27, 31 and 29, 33, or 41 and 40 are significantly different, so that, as a function of the sections of the chambers 37 and 38 and of the stiffness of the spring 36, the movable member of the regulator 14 is pushed into its second position.

The pump 19 through the pipes 17 and 16 feeds the chamber 13 of the jack 8 with fluid under pressure. The rod of the jack 8 is thus, biased outwardly, which brings about a lifting of the working equipment 3 and consequently a return of the front wheels 5 towards the ground 6. When the wheels 5 have regained contact, the relative torque opposing those wheels increases again and the pressure in the pipes 27, 31 and 42 and 41 likewise increases. The movable member of the regulator 14 is then biased towards its intermediate position (third position) under the effect of the return member 36. There has thus been achieved automatically and in a subordinate manner balancing of the tractive forces which act upon the two sets of front wheels 5 and rear wheels 7.

Of course it is easily understood that a similar operation is obtained in the case in which the rear wheels 7 tend to move out of contact with the ground 6. It is not considered necessary to describe in detail the manner of operation, which is very similar to that which has just been described of the machine in this other configuranon.

It may be found desired to neutralise temporarily the above described subordination, for example in the case when, in order to change a front wheel, it is desired effectively to raise this wheel 5 clear of the ground 6 and keep it clear. In order to do this it is sufficient to place the regulator 39 in its second position by action on the lever 45. In that manner the chambers 37 and 38 are put in communication with the reservoir 20 through the pipes 40, 41 and 44. The resilient member 36 alone acts on the movable member of the regulator 14 and returns the movable member permanently into its third position. The pump 19 delivers fluid to the reservoir 20 through; the pipes 17 and 18 and, because the pipes 15 and 16 are blocked at the distributor 14, the chambers 12 and 13 of the jack 8 are isolated and the rod of the said jack 8 is maintained in position with respect to the cylinder. of this jack.

The functioningof the machine which has been describedthus is an automatic control of the opposing torques acting concomitantly on the wheels of the two sets of front 6 and rear wheels 4, and an automatic subordinate adjustment of the position of the working equipment 3 to the values of these opposing torques. In this way the best possible adhesion of the driving wheels 5 and 7 is obtained and consequently, at given power from themachine, the maximum force of penetratiori for thetool 1, without its being necessary for the driver of the machine to have to appreciate the adhesion conditions at the time, or to be particularly experienced in reacting in optimum manner.

Furthermore the circuit of FIG. 3 is considerably simpler than that described in the above referred to US. Pat. No. 3,782,572 in the sense that the regulator 14 and the pump ,19 are used both to supply fluid under pressure to one of the chambers 12 or 13 and place the other chamber in communication with the reservoir 20 by operation on the lever 35, and to subordinate the position of the working equipment 3 to the values of the torques opposing the wheels 5 and 7 by the action of fluid in the chambers 37 and 38 and of the resilient member 36.

In certain cases, it may, however, be desired to pilot" the movable member of the regulator 14 by a lowpressure fluid. This requirement is present particularly when it is desired to obtain simple manufacture of the regulator 14. In this case the circuit of FIG. 3 is slightly modified to interpose an intermediate state of pilotage. Thus one arrives at the arrangement described with reference to FIG. 4. g g

In FIG. 4 the regulator 55 is similar to the regulator 39 of FIG. 3.

It is assumed first of all that the distributor 55 is in its first position. The pressures of the fluids in the feed pipes 27 and 29 to the motors 21 and 22, and consequently in the pipes 31 and 53 and 33 and 54 act to place the movable member of the regulator 49 in one of its positions. For example, when the front wheels 5 have a tendency to lift, the pressure falls in the pipes 27, 31 and 53 so that the regulator 49 is placed in its first position. Fluid delivered to the pipe 56 by the lowpressure pump 57 flows through the pipes 59 and 40 to the chamber 37 while the chamber 38 is placed in communication with the reservoir 20 through the pipes 41 and 62. Thus the regulator 14 is placed in its second position. In this position the fluid delivered by the pump 19 flows to the'chamb'er 13 through the pipes 17 and 16, and fluid contained in the chamber 12 is delivered to the reservoir 20 through the pipes 15 and 18b. As in the previously described embodiment of FIG. 3, the rod of the jack 8 is biased outwardly of the cylinder of this jack and the workingequipment 3 is raised to bring the front wheels 5 back into contact with the ground 6.

Operation of the circuit of FIG. 4 is exactly similar when the rear wheels are raised from the ground. Thus both automatic subordination and subordination by pilotage of the main regulator 14 of the device as FIG. 3 is obtained. However, the regulator 14 is now piloted by the low-pressure fluid delivered by the pump 57 and not directly by the high-pressure fluid in the feed pipes 27 and 29 to the motors 21 and 22. Manufacture of the regulator 14 is, as a result, considerably easier.

When the regulator 55 is placed in its second position flow of the pilotage fluid, delivered to the pipe 56 by the pump 57, is cut off from the regulator 14 and from the chambers 37 and 38. Consequently the chambers are no longer fed with fluid under pressure (under low pressure, moreover) so that the effect of the resilient member 36 becomes preponderant and returns the regulator 14 to its third position. The pipes 15 and 16 are then blocked at the regulator 14 and, because the chambers 12 and 13 of the jack 8 are isolated, the rod of the jack 8 is maintained in position with respect to the cylinder of this jack. Subordination in position is neutralised.

It will be understood that the characteristics of the operation are maintained when the regulators and 26 are arranged not as previously described to make the motors 21 and 22 rotate in the direction for running forwards, but are arranged to make the motors 21 and 22 rotate in the direction for running backwards.

It will be observed that in the various cases in which the pressure of fluid acts either in the chamber 37 or in the chamber 38 the effect of this pressure is sufficiently large to oblige the driver to follow the displacement of the manual control lever 35, so that the operation providing subordination prevails.

I claim:

1. A public works machine comprising:

a frame,

a set of front driving wheels to which at least one first hydraulic driving motor is coupled;

a set of rear driving wheels to which at least one rear hydraulic driving motor is coupled;

means for supplying fluid under pressure to said front and rear motors and connected thereto by respective feed pipes;

a discharge reservoir means;

working equipment articulated to said frame;

a double-acting drive member coupled between said frame and said working equipment and which comprises two chambers;

a first pipe and a second pipe connected respectively to said two chambers;

a three-position regulator comprising the sole valve means for providing work fluid for said doubleacting drive member which:

in a first position connects said first pipe to said fluid supply means and said second pipe to said discharge reservoir means;

in a second position connects said first pipe to said discharge reservoir means and said second pipe to said fluid supply means;

and, in a third position blocks said first and second manually operable means for selecting the position of said regulator;

and, automatically operable control means for automatically positioning said regulator in accordance with the values of the torques opposing said front and rear sets of wheels and comprising a doubleacting drive device having two chambers which are respectively connected to a third pipe and a fourth pipe which can be placed in communication respectively with fluids at pressure corresponding to those in said feed pipe to said front and rear motors, and a return member tending to maintain said regulator in its third position when the effects of the pressure of fluids in said two chambers are equal and opposite.

2. A machine as claimed in claim 1, additionally including a twoosition regulator, in the first position of which corresponds to effective operation of said automatically operable control means in which communication is established between said two chambers of said drive device and fluids at pressures corresponding to those in said feed pipes to said front and rear motors, and in the second position of which said automatically operable control means is taken out of operation and said two chambers of the drive device are placed in communication with said discharge reservoir means.

3. A machine as claimed in claim 2, wherein said feed pipes to said front and rear motors are connectable by said third and fourth pipes to respective one of said chambers of said drive device and said two-position regulator is interposed between said third and fourth pipes and said feed pipes to the front and rear motors, in its first position said regulator placing said third and fourth pipes in communication with said feed pipes, and in its second position said regulator placing said third and fourth pipes in communication with said discharge reservoir means.

4. A machine as claimed in claim 2, wherein said automatically operable control means includes a second three position regulator to which is coupled a second automatically operable means for selection of the position of the second three position regulator in dependance on the values of the torques opposing the front and rear wheels and which comprises a double-acting drive device having two chambers and a return member tending to maintain said second regulator in its third position, when the effects of the pressures of fluids in said two chambers are equal and opposite said two chambers of said second automatically operable device being connected respectively by pipes to said feed pipes to said front and rear motors, and wherein said third and fourth pipes are connected to said second three-position regulator, a fifth pipe connected to means for supplying fluid under pressure and a sixth pipe connected to a discharge reservoir are connected to said second three-position regulator, the three positions of said second three-position regulator correspond to the preponderance of the effect of fluid in one or other of said chambers of said second automatically operable means, or with equality of the said effects, and said second three-position regulator connects said third pipe to said fifth pipe and said fourth pipe to said sixth pipe in its first position, said third pipe to said sixth pipe and said fourth pipe to said fifth pipe, in its second position and said third and fourth pipes to said sixth pipe in its third position and wherein said two-position regulator is arranged in said fifth pipe which it separates into two portions and is connected by a seventh pipe to said discharge reservoir means, in its first position said two-position regulator places said two portions of said fifth pipe to which it is connected in communication in its second position said two-position isolates said two portions of the fifth pipe from one another and places said seventh pipe in communication with that one of said two portions of said fifth pipe which is connected to said second three-position regulator.

5. A machine as claimed in claim 1, wherein said feed pipes to said front and rear motors are respectively connectable by said third and fourth pipes to respective ones of said chambers of said drive device.

6. A machine as claimed in claim 1, wherein said automatically operable control means includes a second three-position regulator to which is coupled a second automatically operable means for selection of the position of the second three-position regulator in dependance on the values of the torques opposing the front and rear wheels and which comprises a double-acting drive device having two chambers and a return member tending to maintain said second regulator in its third position, when the effects of the pressures of fluids in said two chambers are equal and opposite said two chambers of said second automatically operable device being connected respectively by pipes to said feed pipes to said front and rear motors, and wherein said third and fourth pipes are connected to said second three-position regulator, a fifth pipe is connected to means for supplying fluid under pressure and a sixth pipe connected to a discharge reservoir are connected to said second three-position regulator, the three positions of said second three-position regulator correspond to the preponderance of the effect of fluid in one or other of said chambers of said second automatically operable means, or with equality of the said effects, and said second three-position regulator connects said third pipe to said fifth pipe and said fourth pipe to said sixth pipe in its first position, said third pipe to said sixth pipe and said fourth pipe to said fifth pipe, in its second position and said third and fourth pipes to said sixth pipe in its third position. 

1. A public works machine comprising: a frame, a set of front driving wheels to which at least one first hydraulic driving motor is coupled; a set of rear driving wheels to which at least one rear hydraulic driving motor is coupled; means for supplying fluid under pressure to said front and rear motors and connected thereto by respective feed pipes; a discharge reservoir means; working equipment articulated to said frame; a double-acting drive member coupled between said frame and said working equipment and which comprises two chambers; a first pipe and a second pipe connected respectively to said two chambers; a three-position regulator comprising the sole valve means for providing work fluid for said double-acting drive member which: in a first position connects said first pipe to said fluid supply means and said second pipe to said discharge reservoir means; in a second position connects said first pipe to said discharge reservoir means and said second pipe to said fluid supply means; and, in a third position blocks said first and second pipes; manually operable means for selecting the position of said regulator; and, automatically operable control means for automatically positioning said regulator in accordance with the values of the torques opposing said front and rear sets of wheels and coMprising a double-acting drive device having two chambers which are respectively connected to a third pipe and a fourth pipe which can be placed in communication respectively with fluids at pressure corresponding to those in said feed pipe to said front and rear motors, and a return member tending to maintain said regulator in its third position when the effects of the pressure of fluids in said two chambers are equal and opposite.
 2. A machine as claimed in claim 1, additionally including a two-position regulator, in the first position of which corresponds to effective operation of said automatically operable control means in which communication is established between said two chambers of said drive device and fluids at pressures corresponding to those in said feed pipes to said front and rear motors, and in the second position of which said automatically operable control means is taken out of operation and said two chambers of the drive device are placed in communication with said discharge reservoir means.
 3. A machine as claimed in claim 2, wherein said feed pipes to said front and rear motors are connectable by said third and fourth pipes to respective one of said chambers of said drive device and said two-position regulator is interposed between said third and fourth pipes and said feed pipes to the front and rear motors, in its first position said regulator placing said third and fourth pipes in communication with said feed pipes, and in its second position said regulator placing said third and fourth pipes in communication with said discharge reservoir means.
 4. A machine as claimed in claim 2, wherein said automatically operable control means includes a second three position regulator to which is coupled a second automatically operable means for selection of the position of the second three-position regulator in dependance on the values of the torques opposing the front and rear wheels and which comprises a double-acting drive device having two chambers and a return member tending to maintain said second regulator in its third position, when the effects of the pressures of fluids in said two chambers are equal and opposite said two chambers of said second automatically operable device being connected respectively by pipes to said feed pipes to said front and rear motors, and wherein said third and fourth pipes are connected to said second three-position regulator, a fifth pipe connected to means for supplying fluid under pressure and a sixth pipe connected to a discharge reservoir are connected to said second three-position regulator, the three positions of said second three-position regulator correspond to the preponderance of the effect of fluid in one or other of said chambers of said second automatically operable means, or with equality of the said effects, and said second three-position regulator connects said third pipe to said fifth pipe and said fourth pipe to said sixth pipe in its first position, said third pipe to said sixth pipe and said fourth pipe to said fifth pipe, in its second position and said third and fourth pipes to said sixth pipe in its third position and wherein said two-position regulator is arranged in said fifth pipe which it separates into two portions and is connected by a seventh pipe to said discharge reservoir means, in its first position said two-position regulator places said two portions of said fifth pipe to which it is connected in communication in its second position said two-position isolates said two portions of the fifth pipe from one another and places said seventh pipe in communication with that one of said two portions of said fifth pipe which is connected to said second three-position regulator.
 5. A machine as claimed in claim 1, wherein said feed pipes to said front and rear motors are respectively connectable by said third and fourth pipes to respective ones of said chambers of said drive device.
 6. A machine as claimed in claim 1, wherein said automatically operable control means includes a secoNd three-position regulator to which is coupled a second automatically operable means for selection of the position of the second three-position regulator in dependance on the values of the torques opposing the front and rear wheels and which comprises a double-acting drive device having two chambers and a return member tending to maintain said second regulator in its third position, when the effects of the pressures of fluids in said two chambers are equal and opposite said two chambers of said second automatically operable device being connected respectively by pipes to said feed pipes to said front and rear motors, and wherein said third and fourth pipes are connected to said second three-position regulator, a fifth pipe is connected to means for supplying fluid under pressure and a sixth pipe connected to a discharge reservoir are connected to said second three-position regulator, the three positions of said second three-position regulator correspond to the preponderance of the effect of fluid in one or other of said chambers of said second automatically operable means, or with equality of the said effects, and said second three-position regulator connects said third pipe to said fifth pipe and said fourth pipe to said sixth pipe in its first position, said third pipe to said sixth pipe and said fourth pipe to said fifth pipe, in its second position and said third and fourth pipes to said sixth pipe in its third position. 